feat(H001): add decision tree recommendations for invalid indexes

Summary

Extends H001 Invalid Indexes report with a decision tree to recommend whether to DROP, RECREATE, or flag as UNCERTAIN for each invalid index.

Decision Tree

┌───────────────────────────────────────────┐
│ Is there a valid index on same column(s)? │
└─────────────────────┬─────────────────────┘
           ┌──────────┴──────────┐
          YES                    NO
           │                     │
           ▼                     ▼
┌────────────────┐    ┌─────────────────────────┐
│   DROP index   │    │  Backs a constraint?    │
│   (duplicate)  │    │     (UNIQUE / PK)       │
└────────────────┘    └────────────┬────────────┘
                          ┌────────┴────────┐
                         YES                NO
                          │                 │
                          ▼                 ▼
                 ┌────────────┐    ┌─────────────────────┐
                 │  RECREATE  │    │  Table < 10K rows?  │
                 └────────────┘    └──────────┬──────────┘
                                      ┌───────┴───────┐
                                     YES              NO
                                      │               │
                                      ▼               ▼
                             ┌─────────────┐   ┌─────────────┐
                             │    DROP     │   │  UNCERTAIN  │
                             │   monitor   │   │  needs RCA  │
                             └─────────────┘   └─────────────┘

New Fields

Field	Description
is_pk	True if index backs PRIMARY KEY
is_unique	True if index is UNIQUE
constraint_name	Constraint name if any
table_row_estimate	Estimated rows from reltuples
has_valid_duplicate	Valid index on same columns exists
valid_duplicate_name	Name of valid duplicate index
valid_duplicate_definition	CREATE INDEX statement of valid duplicate

Note

Recommendations (DROP, RECREATE, UNCERTAIN) and commands (drop_command, reindex_command) are computed at render time based on the decision tree, not stored in JSON.

Changes

• config/pgwatch-prometheus/metrics.yml: Extended SQL query to gather decision data
• reporter/schemas/H001.schema.json: Extended schema with new fields
• cli/lib/checkup.ts: Express mode decision logic
• reporter/postgres_reports.py: Full mode decision logic

Test Plan

• Verify H001 report generates correctly in full mode
• Verify H001 report generates correctly in express mode
• Test with invalid index that has valid duplicate → should recommend DROP
• Test with invalid PK/UNIQUE index → should recommend RECREATE
• Test with invalid index on small table (< 10K rows) → should recommend DROP
• Test with invalid index on large table → should recommend UNCERTAIN
• Verify JSON schema validation passes

🤖 Generated with Claude Code

Issue: https://gitlab.com/postgres-ai/platform/-/issues/346